Merck said the foil pouches holding Liptruzet pills could allow air and moisture inside, potentially decreasing the drug's effectiveness.

The recall covers all four dose strengths and every batch that's gone out since Liptruzet hit the market in May.

Liptruzet combines two medications that work together to reduce "bad" cholesterol levels:

Atorvastatin, the generic version of the widely used cholesterol medication Lipitor, which reduces the body's natural cholesterol production, and

Zetia (ezetimibe), a Merck-produced drug that decreases the amount of cholesterol absorbed from food.

Cardiologists expect no health problems to result from the recall, in part because both atorvastatin and Zetia will remain available separately.

"Patients are not going to be in any harm's way just going on atorvastatin until this packaging issue gets corrected," said Dr. Kevin Marzo, chief of cardiology at Winthrop-University Hospital in Mineola, N.Y.

Marzo added that since the drug has been out for just a matter of months, it's unlikely that doctors have been prescribing it widely.

If a doctor feels a patient needs the combination treatment, then the doctor can prescribe both drugs individually and the patient can take two pills, said Dr. Deepak Bhatt, executive director of Interventional Cardiovascular Programs at Brigham and Women's Hospital Heart and Vascular Center, in Boston.

Patients can continue to take any Liptruzet they already have on hand, according to Merck, and should talk with their doctor before they quit taking it.

Bhatt said the real risk of this recall is that patients will hear about it and stop taking their cholesterol medication altogether.

"It should be relatively simple and even cheaper to substitute atorvastatin," Bhatt said. "Bottom line, this is something that can be addressed in a relatively straightforward way. The key is not to say, 'Well, I don't have to take anything in its place.'"

Liptruzet and Zetia each cost more than $5.50 per pill, while atorvastatin costs about a quarter per pill.

Merck said it plans to get Liptruzet back on the market as soon as possible.